1. Field of the Invention
The present invention relates to guidance systems, and more particularly to guidance systems responsive to the lateral displacement of a guided object from the center of an electromagnetic signal generated by elongated conductor loops excited in guadrature by an A.C. electrical signal source.
2. Description of the Prior Art
Automatic guidance systems typically take on a variety of forms, the more complex of such forms being guidance systems which control a moving object both along a preselected path and according to a predetermined sequence of velocities. The less complex guidance systems, having generally a wider potential application in commercial use, are guidance systems which control the lateral displacement of the object along a predetermined path. Generally such guidance systems are signal following systems where the attitude of the object is controlled in response to lateral deviations thereof from the signal center and the resulting dynamics of motion of the object complete in the guidance loop. In applications where the attitude produced control power of the guided object is weak in comparison with the inertia of the object, such as the applications where a relatively large displacement boat is controlled to follow a particular signal track, large amounts of lead or anticipation are necessary in order to control the lateral accuracy of the boat path. Furthermore, even if anticipated, the corrective dynamics of motion are typically underdamped and of low frequency, resulting in large corrective overshoots. Even if augmented to reduce the overshoots the overall gain of such systems is typically low and many attempts have been made in the past to reduce the overall loop errors. One major contributor producing a low loop gain has been the sensor system which functions to identify the tracked signal center as well as any deviations therefrom.
Thus in guidance applications where a mobile object is directed to follow a preselected signal track the signal pick-offs or sensors determining the signal center and the relative lateral location of the object are typically the limiting constraints on the overall tracking accuracy of the system. Such guidance loops depend on a linear displacement from the signal center and accordingly the inherent characteristics of the loop are those of a first order servo having the typical steady state errors which are a function of the loop gain and therefore the sensitivity of the sensors. Control systems of this kind, when utilized for public conveyance purposes, must, however, be both accurate and highly reliable to properly perform stationing functions such as docking at loading platforms. Heretofore most prior art guidance systems adapted for commercial use entailed elaborate sensors requiring extensive augmentation, control power and maintenance and care in operation. Furthermore, most such sensing devices were amplitude responsive and therefore sensitive to signal attenuation or drop off through any medium, while also being constantly driven at maximum loop gain, there being no convenient means for passively controlling gain where higher accuracy was required. Particularly when applied to amusement vehicles such as guided boats floating or propelled along preselected channels in waters which are heavily saturated with various contaminants thrown there by the passengers, such boats being loaded to varying displacement depths, a guidance system which is simple and inherently insensitive to the varying attenuation through the medium is desirable.